Process and device for measuring physical characteristics of a porous sample by centrifugal displacement of fluids

Abstract

The invention is a process and device for performing successive drainage and imbibition phases of a first electrically-conducting fluid and a second fluid of lower density than the first fluid, in a porous sample (1) by means of a centrifuge. Each sample is placed in a main chamber (3) of an elongate vessel (2) fastened to the end of an arm of the centrifuge, together with a spacer (6) whose volume is so selected that, on the one hand, the interface between the two fluids does not come into contact with the sample in operation and, on the other hand, the volume of chamber (3) remaining free around the sample and the associated spacer is greater than, but preferably close to the pore volume of the sample, so as to maximize the displacement amplitude of the interface for a given variation of the volume of fluid displaced. A capacitive sonde (11) in an auxiliary cavity (4), connected to an outer measuring device, is used for measuring the displacements of the interface. The invention has applications of surveying of rocks taken from an underground reservoir.

What is claimed is:  
     
       1. A process for measuring physical characteristics of a porous solid sample by performing drainage and imbibition operations on the porous sample in a presence of a first electrically-conductive fluid and of a second fluid of lower density than the first fluid, using a centrifugation assembly including at least one vessel provided with a chamber, each vessel being fastened to an end of an arm secured to a hub, and a rotational drive which drives each arm in rotation to create centrifugal force exerted in a radial direction along each vessel, comprising: 
       providing drainage and imbibition operations by centrifuging each vessel at a centrifugation speed which increases by steps until a capillary equilibrium is reached for each step, with the porous sample being positioned in each chamber together with a spacer made of a non porous material, the spacer volume being so selected that, in operation, the interface between the two fluids does not come into contact with the sample, after injecting a known amount of one of the first electrically-conductive fluid and the second fluid of a lower density into each chamber on a side thereof occupied by the spacer, with respective positions of the sample and of the associated spacer in each chamber being inverted according to whether the drainage operation or the imbibition operation is performed.  
     
     
       2. A process for measuring physical characteristics of a porous solid sample by performing drainage operations, in a presence of a first electrically-conductive fluid and of a second fluid of lower density than the first electrically-conductive fluid using a centrifugation assembly including at least one vessel each provided with a chamber, each vessel being fastened to an arm secured to a hub, a rotational drive which drives each arm in rotation which creates centrifugal force exerted in a radial direction along each vessel, a sonde for detecting, in each vessel, an interface between the first electrically-conductive fluid and the second fluid of a lesser density and a system, responsive to each sonde, which determines a volume of fluid channel drained from the sample, comprising: 
       a) placing in each chamber filled with a volume of the second fluid of a lesser density a sample previously saturated with the first electrically-conductive fluid and a spacer made of a nonporous material with the spacer positioned so as to be at a different distance from the hub than the sample;  
       b) injecting a known amount of the first electrically-conductive fluid into each chamber on the side thereof occupied by the spacer;  
       c) centrifugating each vessel at a centrifugation speed which increases by steps until a capillary equilibrium is reached for each step;  
       d) acquiring, during centrifuging, signals from each sonde representative of level variations of an interface between the first electrically-conductive fluid and the second fluid of lower density; and  
       e) determining with the system a volume of the first fluid drained from the sample.  
     
     
       3. A process as claimed in claim  2 , further comprising: 
       removing the first electrically-conductive fluid from each vessel by injecting a volume of the second fluid of lower density;  
       measuring a volume of removed first electrically-conductive fluid; and  
       comparing the measured volume of the first electrically-conductive fluid with the volume determined by the system.  
     
     
       4. A process as claimed in claim  2 , comprising: 
       a) placing in each chamber filled with a volume of the first electrically-conductive fluid a sample and a spacer made of a nonporous material, with the spacer positioned so as to be at a nearer distance from the hub than the sample;  
       b) injecting a known amount of the second fluid of lower density into each chamber on the side thereof occupied by the spacer;  
       c) centrifugating each vessel at a centrifugation speed which increases by steps until a capillary equilibrium is reached for each step;  
       d) acquiring, while centrifuging each vessel, signals from each sonde representative of level variations of an interface between the first electrically-conductive fluid and the second fluid of lower density; and  
       e) determining with the system a volume of the first electrically-conductive fluid imbibed by the sample.  
     
     
       5. A process as claimed in claim  3 , comprising: 
       a) placing in each chamber filled with a volume of the first electrically-conductive fluid a sample and a spacer made of a nonporous material, with the spacer positioned so as to be at a nearer distance from the hub than the sample;  
       b) injecting a known amount of the second fluid of lower density into each chamber on the side thereof occupied by the spacer;  
       c) centrifugating each vessel at a centrifugation speed which increases by steps until a capillary equilibrium is reached for each step;  
       d) acquiring, while centrifuging each vessel, signals from each sonde representative of level variations of an interface between the first electrically-conductive fluid and the second fluid of lower density; and  
       e) determining with the system a volume of the first electrically-conductive fluid imbibed by the sample.  
     
     
       6. A process as claimed in claim  4 , further comprising: 
       removing the second fluid of lower density from each vessel by injecting a volume of the first electrically-conductive fluid;  
       measuring a volume of removed second fluid of lesser density; and  
       comparing the measured volume of the second fluid of lower density fluid with the volume of the first electrically-conductive fluid determined with the system.  
     
     
       7. A process as claimed in claim  5 , further comprising: 
       removing the second fluid of lower density from each vessel by injecting a volume of the first electrically-conductive fluid;  
       measuring a volume of removed second fluid of lesser density; and  
       comparing the measured volume of the second fluid of lower density fluid with the volume of the first electrically-conductive fluid determined with the system.  
     
     
       8. A process for measuring physical characteristics of a porous solid sample in a presence of a non-electrically-conducting fluid and a non-electrically-conducting gas, by using a centrifugation assembly including at least one vessel provided with a chamber, each vessel being fastened to the end of an arm secured to a hub, a rotational drive which drives each arm in rotation which creates centrifugal force exerted in a radial direction along each vessel, a sonde which detects, in each vessel, an interface between the non-electrically-conducting fluid and the non-electrically-conducting gas and a system, responsive to each sonde, which determines a position of the interface in each vessel, comprising: 
       placing the sample saturated with the non-electrically-conductive fluid in the at least one vessel filled with the non-electrically-conductive gas;  
       placing a spacer made of a nonporous material in a container, made of an insulating material positioned in the at least one vessel with the spacer positioned at a farther distance from the hub than the sample, to collect the non-electrically-conductive fluid drained from the sample;  
       injecting a volume of the non-electrically-conductive fluid in each container;  
       centrifugating the at least one vessel at a centrifugation speed which increased by steps until a capillary equilibrium is reached for each step; and  
       measuring with the system a displacement of an interface between the non-electrically-conductive fluid and the non-electrically-conductive gas.  
     
     
       9. A device for measuring physical characteristics of a porous solid sample by performing drainage phases, in a presence of a first electrically-conductive fluid and of a second fluid of lower density than the first fluid comprising: 
       a centrifugation assembly including at least one vessel provided with a main chamber, each vessel being fastened to an end of an arm secured to a hub, a rotational drive which drives each arm in rotation to produce centrifugal force exerted in a radial direction along each vessel, a detector which detects a position, in a side chamber of each vessel, of an interface between the first electrically-conductive fluid and the second fluid of lower density, a spacer disposed in each main chamber made of a nonporous material with the volume of the spacer being selected so that, in operation, the interface between the first electrically-conductive fluid and the second fluid of a lower density does not come into contact with the sample, the detector in each vessel including a sonde with a metallic rod coated with a layer of a dielectric material, each sonde being placed in the side chamber having a conducting wall adjacent the main chamber and a system, outside the centrifuging assembly, connected with each sonde through a rotating electric connector which measures capacitance variation detected by each sonde in contact with the first electrically-conductive fluid and the second fluid of lower density in each vessel resulting from an immersion thereof in the first electrically-conductive fluid, and which determines a volume of fluid displaced.  
     
     
       10. A device as claimed in claim  9 , further comprising: 
       a container in each vessel, made of an insulating material, which receives the spacer, having a cross-section larger than a cross-section of the spacer, the container being positioned for collecting fluid expelled from the sample, with the container communicating with the side chamber.  
     
     
       11. A device as claimed in claim  10 , wherein: 
       each container has a volume so that a total volume of the second fluid of lower density expelled from the sample substantially fills up a free volume in the container around the spacer so that a range of displacement of the interface resulting from a variation of volume of the first electrically-conductive fluid and the second fluid of lower density in the first chamber is maximized.  
     
     
       12. A device as claimed in claim  9 , wherein each vessel comprises: 
       two channels communicating during rotation on opposite ends of each main chamber with an outside of an end of the vessel closest to the hub; and  
       caps which insulate an inside of each main chamber during centrifugation.  
     
     
       13. A device as claimed in claim  10 , wherein: 
       two channels communicating during rotation on opposite ends of each main chamber with an outside of an end of the vessel closest to the hub; and  
       caps which insulate an inside of each main chamber during centrifugation.  
     
     
       14. A device as claimed in claim  11 , wherein: 
       two channels communicating during rotation on opposite ends of each main chamber with an outside of an end of the vessel closest to the hub; and  
       caps which insulate an inside of each main chamber during centrifugation.  
     
     
       15. A device as claimed in claim  9 , wherein the centrifugation assembly comprises: 
       at least one pair of arms and vessels placed in opposition at ends respectively of the at least one pair of arms; and  
       a pair of samples associated with each pair of arms.  
     
     
       16. A device as claimed in claim  10 , wherein the centrifugation assembly comprises: 
       at least one pair of arms and vessels placed in opposition at ends respectively of the at least one pair of arms; and  
       a pair of samples associated with each pair of arms.  
     
     
       17. A device as claimed in claim  16 , wherein the centrifugation assembly comprises: 
       at least one pair of arms and vessels placed in opposition at ends respectively of the at least one pair of arms; and  
       a pair of samples associated with each pair of arms.  
     
     
       18. A process as claimed in claim  2  wherein: 
       the spacer is positioned so as to be at distance farther from the hub than the sample.  
     
     
       19. A process as claimed in claim  3  wherein: 
       the spacer is positioned so as to be at distance farther from the hub than the sample.